This invention relates principally to a fluid film bearing and to a process for its production.
It is known to provide a bearing comprising a shaft capable of rotating with respect to a casing. When stopped, a plurality of sheets is applied against the shaft forming wedges containing a fluid, for example air. The rotation of the shaft with respect to the sheets causes compression of the wedge of fluid creating a pressure cell. This results in the formation of a film of fluid between the sheets and the shaft. Once the film of fluid is formed, the bearing presents a very low resistance coupling and no wear of the sheets.
For good operation of the bearing, it is imperative that the fluid film between the sheets and the shaft never be destroyed, in particular by unbalance of the bearing, by the weight of the shaft, by vibrations, by acceleration and by the gyroscopic effects resulting from the rotation of the shaft or of the casing and the displacement of the bearing, for example rising in an aircraft.
In bearings of the known type, the stability of the fluid film is obtained by a radial rigidity or stiffness of the sheets which compress the fluid film.
This type of system presents a number of disadvantages.
The application force of the sheets against the shaft increases the resistance of the bearing to start of rotation.
For overcoming these disadvantages, it is known to cover the sheets with a solid layer limiting the coefficient of friction between the sheets and the shaft.
In spite of this, the sizeable resistance to starting causes:
a significant wear of the sheets,
a consumption of energy upon starting,
a heating at the start risking deterioration of the lubricating layers,
a starting of the bearing at a higher speed.
Moreover, the radial stiffness of the sheets does not permit operation of the bearing at low speeds, since the film of air only forms at higher speeds.
In a bearing according to the present invention, the radial stiffness of the sheets is optimized, in particular at low speeds. The optimization of the radial stiffness of the sheets is permitted, if it proves necessary, by the presence of external restraining elements permitting maintaining a radial stiffness of the bearing when the sheets are separated from the shaft by the formation of the fluid film.